1、Designation: D5490 93 (Reapproved 2014)1Standard Guide forComparing Groundwater Flow Model Simulations to Site-Specific Information1This standard is issued under the fixed designation D5490; the number immediately following the designation indicates the year oforiginal adoption or, in the case of re
2、vision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1NOTEReapproved with editorial changes in October 2014.1. Scope1.1 This guide covers techniques that should be
3、 used tocompare the results of groundwater flow model simulations tomeasured field data as a part of the process of calibrating agroundwater model. This comparison produces quantitativeand qualitative measures of the degree of correspondencebetween the simulation and site-specific information relate
4、d tothe physical hydrogeologic system.1.2 During the process of calibration of a groundwater flowmodel, each simulation is compared to site-specific informa-tion such as measured water levels or flow rates. The degree ofcorrespondence between the simulation and the physical hy-drogeologic system can
5、 then be compared to that for previoussimulations to ascertain the success of previous calibrationefforts and to identify potentially beneficial directions forfurther calibration efforts.1.3 By necessity, all knowledge of a site is derived fromobservations. This guide does not address the adequacy o
6、f anyset of observations for characterizing a site.1.4 This guide does not establish criteria for successfulcalibration, nor does it describe techniques for establishingsuch criteria, nor does it describe techniques for achievingsuccessful calibration.1.5 This guide is written for comparing the resu
7、lts ofnumerical groundwater flow models with observed site-specificinformation. However, these techniques could be applied toother types of groundwater related models, such as analyticalmodels, multiphase flow models, noncontinuum (karst orfracture flow) models, or mass transport models.1.6 This gui
8、de is one of a series of guides on groundwatermodeling codes (software) and their applications.1.7 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health pr
9、actices and determine the applica-bility of regulatory limitations prior to use.1.8 This guide offers an organized collection of informationor a series of options and does not recommend a specificcourse of action. This document cannot replace education orexperience and should be used in conjunction
10、with professionaljudgment. Not all aspects of this guide may be applicable in allcircumstances. This ASTM standard is not intended to repre-sent or replace the standard of care by which the adequacy ofa given professional service must be judged, nor should thisdocument be applied without considerati
11、on of a projects manyunique aspects. The word “Standard” in the title of thisdocument means only that the document has been approvedthrough the ASTM consensus process.2. Referenced Documents2.1 ASTM Standards:2D653 Terminology Relating to Soil, Rock, and ContainedFluids3. Terminology3.1 Definitions:
12、3.1.1 For common definitions of terms in this standard, referto Terminology D653.3.2 Definitions of Terms Specific to This Standard:3.2.1 application verificationusing the set of parametervalues and boundary conditions from a calibrated model toapproximate acceptably a second set of field data measu
13、redunder similar hydrologic conditions.3.2.1.1 DiscussionApplication verification is to be distin-guished from code verification which refers to software testing,comparison with analytical solutions, and comparison with1This guide is under the jurisdiction ofASTM Committee D18 on Soil and Rockand is
14、 the direct responsibility of Subcommittee D18.21 on Groundwater andVadose Zone Investigations.Current edition approved Oct. 1, 2014. Published October 2014. Originallyapproved in 1993. Last previous edition approved in 2008 as D5490 93 (2008).DOI: 10.1520/D5490-93R14E01.2For referenced ASTM standar
15、ds, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 1
16、9428-2959. United States1other similar codes to demonstrate that the code represents itsmathematical foundation.3.2.2 calibrationthe process of refining the model repre-sentation of the hydrogeologic framework, hydraulicproperties, and boundary conditions to achieve a desireddegree of correspondence
17、 between the model simulations andobservations of the groundwater flow system.3.2.3 censored dataknowledge that the value of a variablein the physical hydrogeologic system is less than or greaterthan a certain value, without knowing the exact value.3.2.3.1 DiscussionFor example, if a well is dry, th
18、en thepotentiometric head at that place and time must be less than theelevation of the screened interval of the well although itsspecific value is unknown.3.2.4 conceptual modelan interpretation or working de-scription of the characteristics and dynamics of the physicalsystem.3.2.5 groundwater flow
19、modelan application of a math-ematical model to represent a groundwater flow system.3.2.6 hydrologic conditiona set of groundwater inflows oroutflows, boundary conditions, and hydraulic properties thatcause potentiometric heads to adopt a distinct pattern.3.2.7 residualthe difference between the com
20、puted andobserved values of a variable at a specific time and location.3.2.8 simulationin groundwater flow modeling, one com-plete execution of a groundwater modeling computer program,including input and output.3.2.8.1 DiscussionFor the purposes of this guide, a simu-lation refers to an individual m
21、odeling run. However, simula-tion is sometimes also used broadly to refer to the process ofmodeling in general.4. Summary of Guide4.1 Quantitative and qualitative comparisons are both es-sential. Both should be used to evaluate the degree of corre-spondence between a groundwater flow model simulatio
22、n andsite-specific information.4.2 Quantitative techniques for comparing a simulation withsite-specific information include:4.2.1 Calculation of residuals between simulated and mea-sured potentiometric heads and calculation of statistics regard-ing the residuals. Censored data resulting from detecti
23、on of dryor flowing observation wells, reflecting information that thehead is less than or greater than a certain value withoutknowing the exact value, should also be used.4.2.2 Detection of correlations among residuals. Spatial andtemporal correlations among residuals should be investigated.Correla
24、tions between residuals and potentiometric heads canbe detected using a scattergram.4.2.3 Calculation of flow-related residuals. Model resultsshould be compared to flow data, such as water budgets,surface water flow rates, flowing well discharges, verticalgradients, and contaminant plume trajectorie
25、s.4.3 Qualitative considerations for comparing a simulationwith site-specific information include:4.3.1 Comparison of general flow features. Simulationsshould reproduce qualitative features in the pattern of ground-water contours, including groundwater flow directions,mounds or depressions (closed c
26、ontours), or indications ofsurface water discharge or recharge (cusps in the contours).4.3.2 Assessment of the number of distinct hydrologicconditions to which the model has been successfully calibrated.It is usually better to calibrate to multiple scenarios, if thescenarios are truly distinct.4.3.3
27、 Assessment of the reasonableness or justifiability ofthe input aquifer hydrologic properties given the aquifermaterials which are being modeled. Modeled aquifer hydro-logic properties should fall within realistic ranges for thephysical hydrogeologic system, as defined during conceptualmodel develop
28、ment.5. Significance and Use5.1 During the process of calibration of a groundwater flowmodel, each simulation is compared to site-specific informa-tion to ascertain the success of previous calibration efforts andto identify potentially beneficial directions for further calibra-tion efforts. Procedur
29、es described herein provide guidance formaking comparisons between groundwater flow model simu-lations and measured field data.5.2 This guide is not meant to be an inflexible description oftechniques comparing simulations with measured data; othertechniques may be applied as appropriate and, after d
30、ueconsideration, some of the techniques herein may be omitted,altered, or enhanced.6. Quantitative Techniques6.1 Quantitative techniques for comparing simulations tosite-specific information include calculating potentiometrichead residuals, assessing correlation among head residuals, andcalculating
31、flow residuals.6.1.1 Potentiometric Head ResidualsCalculate the residu-als (differences) between the computed heads and the measuredheads:ri5 hi2 Hi(1)where:ri= the residual,Hi= the measured head at point i,hi= the computed head at the approximate location whereHiwas measured.If the residual is posi
32、tive, then the computed head was toohigh; if negative, the computed head was too low. Residualscannot be calculated from censored data.NOTE 1For drawdown models, residuals can be calculated fromcomputed and measured drawdowns rather than heads.NOTE 2Comparisons should be made between point potentiom
33、etricheads rather than groundwater contours, because contours are the result ofinterpretation of data points and are not considered basic data in and ofthemselves.3Instead, the groundwater contours are considered to reflectfeatures of the conceptual model of the site. The groundwater flow model3Cool
34、ey, R. L., and Naff, R. L., “Regression Modeling of Ground-Water Flow,”USGS Techniques of Water Resources Investigations , Book 3, Chapter B4, 1990.D5490 93 (2014)12should be true to the essential features of the conceptual model and not totheir representation.NOTE 3It is desirable to set up the mod
35、el so that it calculates heads atthe times and locations where they were measured, but this is not alwayspossible or practical. In cases where the location of a monitoring well doesnot correspond exactly to one of the nodes where heads are computed inthe simulation, the residual may be adjusted (for
36、 example, computed headsmay be interpolated, extrapolated, scaled, or otherwise transformed) foruse in calculating statistics. Adjustments may also be necessary when thetimes of measurements do not correspond exactly with the times whenheads are calculated in transient simulations; when many observe
37、d headsare clustered near a single node; where the hydraulic gradient changessignificantly from node to node; or when observed head data is affected bytidal fluctuations or proximity to a specified head boundary.6.1.2 Residual StatisticsCalculate the maximum andminimum residuals, a residual mean, an
38、d a second-orderstatistic, as described in the following sections.6.1.2.1 Maximum and Minimum ResidualsThe maximumresidual is the residual that is closest to positive infinity. Theminimum residual is the residual closest to negative infinity. Oftwo simulations, the one with the maximum and minimumre
39、siduals closest to zero has a better degree of correspondence,with regard to this criterion.NOTE 4When multiple hydrologic conditions are being modeled asseparate steady-state simulations, the maximum and minimum residualcan be calculated for the residuals in each, or for all residuals in allscenari
40、os, as appropriate. This note also applies to the residual mean (see6.1.2.2) and second-order statistics of the residuals (see 6.1.2.4).6.1.2.2 Residual MeanCalculate the residual mean as thearithmetic mean of the residuals computed from a givensimulation:R 5(i51nrin(2)where:R = the residual mean an
41、dn = the number of residuals.Of two simulations, the one with the residual mean closest tozero has a better degree of correspondence, with regard to thiscriterion (assuming there is no correlation among residuals).6.1.2.3 If desired, the individual residuals can be weightedto account for differing d
42、egrees of confidence in the measuredheads. In this case, the residual mean becomes the weightedresidual mean:R 5(i51nwirin(i51nwi(3)where wiis the weighting factor for the residual at point i.The weighting factors can be based on the modelers judgmentor statistical measures of the variability in the
43、 water levelmeasurements. A higher weighting factor should be used for ameasurement with a high degree of confidence than for onewith a low degree of confidence.NOTE 5It is possible that large positive and negative residuals couldcancel, resulting in a small residual mean. For this reason, the resid
44、ualmean should never be considered alone, but rather always in conjunctionwith the other quantitative and qualitative comparisons.6.1.2.4 Second-Order StatisticsSecond-order statisticsgive measures of the amount of spread of the residuals aboutthe residual mean. The most common second-order statisti
45、c isthe standard deviation of residuals:s 5H(i51nri2 R!2n 2 1!J12(4)where s is the standard deviation of residuals. Smaller valuesof the standard deviation indicate better degrees of correspon-dence than larger values.6.1.2.5 If weighting is used, calculate the weighted standarddeviation:s 55(i51nwi
46、ri2 R!2n 2 1!(i51nwi612(5)NOTE 6Other norms of the residuals are less common but may berevealing in certain cases.4,5For example, the mean of the absolute valuesof the residuals can give information similar to that of the standarddeviation of residuals.NOTE 7In calculating the standard deviation of
47、residuals, advancedstatistical techniques incorporating information from censored data couldbe used. However, the effort would usually not be justified because thestandard deviation of residuals is only one of many indicators involved incomparing a simulation with measured data, and such a refinemen
48、t in oneindicator is unlikely to alter the overall assessment of the degree ofcorrespondence.6.1.3 Correlation Among ResidualsSpatial or temporalcorrelation among residuals can indicate systematic trends orbias in the model. Correlations among residuals can beidentified through listings, scattergram
49、s, and spatial or tempo-ral plots. Of two simulations, the one with less correlationamong residuals has a better degree of correspondence, withregard to this criterion.6.1.3.1 ListingsList residuals by well or piezometer, in-cluding the measured and computed values to detect spatial ortemporal trends. Figs. X1.1 and X1.2 present example listingsof residuals.6.1.3.2 ScattergramUse a scattergram of computed versusmeasured heads to detect trends in deviations. The scattergramis produced with measured heads on the abscissa (horizontalaxis) and compute
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